The present invention relates to an anti-lock control apparatus for an air over hydraulic brake system.
An anti-lock control apparatus for an air over hydraulic brake system is conventionally known, as shown in FIG. 4. This anti-lock control apparatus is arranged as follows: A brake valve 2 is connected to an air pressure source 1, while the brake valve 2 is connected to an pneumatic chamber 13 of an air master cylinder 10 through a first air pressure line 4. A hydraulic chamber 14 of the air master cylinder 10 is connected to a liquid input port 21 of a modulator 20, and a check valve is interposed in a passage between the liquid input port 21 of the modulator 20 and a liquid output port 22 thereof. This check valve is arranged such as to be capable of being opened by a hydraulic piston fitted in the modulator 20. A pneumatic piston is connected to the hydraulic piston, and the liquid output port 22 of the modulator 20 is communicated with the hydraulic chamber of the modulator 20 and is connected to a wheel cylinder 26. The pneumatic chamber of the modulator 20 is connected to the first air pressure line 4 via a hold valve 41 constituted by a normally open-type solenoid valve so as to form a second air pressure line 40. In addition, the pneumatic chamber of the modulator 20 is connected to an external part via a decay valve 42 constituted by a normally close-type solenoid valve. In addition, Japanese Patent Publication No. 1824/1976 (a Japanese application based on West German Patent No. 2040206.6) is known as another prior art.
With the control apparatus shown in FIG. 4, since the modulator 20 is provided for anti-lock control, the second air pressure line 40 branching off from the first air pressure line 4 and leading to the modulator 20 is required in addition to the first air pressure line 4 extending from the brake valve 2 to the air master cylinder 10. For this reason, there has been a drawback in that the internal volumes of the air pipes and the modulator 20 increase, with the result that the rising rate of the braking hydraulic pressure during braking and the falling rate of the braking hydraulic pressure during release of braking decrease, and that the amount of air consumed increases.